The present invention relates to extraction between materials of differing densities. More particularly, this invention relates to liquid-liquid or liquid-solid extraction between materials of differing densities in which parallel plate assemblies are advantageously used.
The use of inclined parallel plates to create restricted flow channels for the purposes of expediting phase separation (e.g., oil or sand from water) by density differences is today a well-known practice. The narrow flow channels both discourage turbulence and minimize settling distances, thereby speeding the separation process.
One of the earlier processes (U.S. Pat. No. 2,755,302) disclosed the co-current (one feed) separation of heavy, insoluble nitroglycerine compounds from wash waters.
The value of co-current parallel plate separators was widely recognized when world concern for both cleaner waste waters and conserving crude and waste oils called attention to the need for simple phase separating devices. Thus, devices using assemblies of parallel plates for separating or clarifying single feed streams abound, often with an evolution of specialization offering better efficiency at specific functions. For example, U.S. Pat. No. 3,795,091 discloses a method of assembling plates in modular units for use in separators. U.S. Pat. No. 3,903,000 details a device to utilize parallel plates to settle impurities from a water feed-stream. U.S. Pat. No. 3,933,654 discloses a device to use parallel plates to separate and recover oil from a liquid feed stream. U.S. Pat. No. 4,089,782 describes a method to distribute the feed stream to the parallel plate assembly, and modifies the plate ends to better catch and separate oil from the feed stream.
In addition, U.S. Pat. No. 4,120,796 discloses a device with a settling chamber prior to the plate assembly. The ends of the plates in the assembly are modified to offer better separation and less re-entrainment into the clarified flow. U.S. Pat. No. 4,120,797 describes a system which involves settling at 90.degree. to the feed flow direction by tilting the plates in a different direction. U.S. Pat. No. 4,132,651 discloses a weir to create better feed distribution to the parallel plates. U.S. Pat. No. 4,120,791 and U.S. Pat. No. 4,290,898 describe the use of parallel plate assemblies as auxiliary devices to settle the heavy portion of the feed into traditional pond clarifiers.
In all of the above-noted cases, the system disclosed is used in a co-current flow scheme for dividing into its components a single feed stream directed into the parallel plate assembly. It would be advantageous to provide a system and method for counter-current extraction using parallel plate assemblies.
U.S. Pat. Nos. 4,268,484 and 4,292,277 disclose the use of a plurality of pairs of vertically aligned parallel plates in a multistage co/counter current extractor wherein each pair of plate assemblies involves a plate assembly positioned above an agitated volume and a plate assembly positioned below the agitator volume. The agitated dispersion enters the non-turbulent flow channels between the plates (lighter dispersion rising into the top plate assembly, while heavier dispersion settles to the bottom assembly) where separation occurs. Light phase, disengaged of heavier material, rises through the top assembly to a collection chamber from which it overflows and is ducted into the next agitated volume, while the heavier material settles back into the original agitated volume. Heavy phase settles through the bottom assembly, disengaging itself of light material which rises back into the agitation area, and enters a collecting chamber from which it overflows a weir or is ducted to the next agitation stage in a direction co or counter-current to the lighter phase flow.
In both U.S. Pat. Nos. 4,268,484 and 4,292,277 each pair of parallel plate assemblies is utilized in the traditional separator-clarifier-settler mode with mixed feed entering the flow passages between the parallel plates in one direction (from the agitation chamber) to have phase separation occur with the subsequent passage of a more-or-less purified "disengaged" phase. It would be advantageous to provide an extraction system and method using parallel plate assemblies which utilize a reduced number of plate assemblies for a given degree of extraction, and which system is not complex, is easy to fabricate, operate and maintain, and is flexible to meet varied process requirements.
Therefore, one object of the present invention is to provide an improved apparatus useful for conducting extraction between materials of differing densities.
Another object of the present invention is to provide an improved method for extraction between materials of differing densities. Other objects and advantages of the present invention will become apparent hereinafter.
An improved apparatus useful for conducting extraction between a relatively heavy, solid or liquid first material and a relatively light, solid or liquid second material has been discovered. Extraction methods using such apparatus provide outstandingly advantageous results.
Before proceeding with the description of the present invention, the term "extraction" as used herein is to be considered in its broad context. That is, as used herein, the term "extraction" refers to any situation in which the relatively heavy material leaving the extraction zone includes more or less of at least one component than the relatively heavy material entering the extraction zone and, conversely, the relatively light material leaving the extraction zone includes less or more of such component (s) (or its precursor (s)) than the relatively light material entering the extraction zone. Such physical/chemical mass transfer operations as extraction, leaching, adsorption, absorption, desorption and the like are included within the scope of the term "extraction" as used herein.
One aspect of the present invention, particularly useful when at least one of the materials is liquid and counter-current extraction is envisioned, involves the following apparatus which comprises:
(a) An elongated vessel means including first and second ends, first and second end walls, first and second side walls and a bottom wall;
(b) A first outlet means located at or near the first end of the vessel means for removing relatively light material from the vessel means;
(c) A second outlet means located at or near the second end of the vessel means for removing relatively heavy material from the vessel means;
(d) A first parallel plate assembly means located in the vessel means near the first end of the vessel means and acting to produce the relatively light material to be removed via the first outlet means;
(e) At least one, and preferably a plurality of, intermediate parallel plate assembly means located in the vessel means substantially horizontally spaced away from the first parallel plate assembly means, and preferably from each other, and acting to provide a degree of material separation based on material density;
(f) A second parallel plate assembly means located in the vessel means substantially horizontally spaced away from the intermediate parallel plate assembly means, located near the second end of the vessel means and acting to produce the relatively heavy material to be removed via the second outlet means;
(g) First inlet means located relatively near the first end of the vessel means and acting to introduce the first (feed) liquid or solid, relatively heavy material into the vessel means;
(h) Second inlet means located relatively near the second end of the vessel means and acting to introduce the second (feed) liquid or solid, relatively light material into the vessel means; and
(i) A plurality of agitation means at least one of the agitation means being located in each space between the parallel plate assembly means to facilitate contact between the materials present in such space.
In another aspect, the present invention involves an apparatus useful for co-current extraction of liquid-liquid materials or liquid-solid materials wherein the materials involved in the extraction have mutually different densities. In this instance, the present apparatus comprises:
(a) An elongated vessel means as described above;
(b) Inlet means located at or near the first end of the vessel to introduce a first relatively heavy material and a second relatively light material into the vessel means;
(c) At least one parallel plate assembly means located in the vessel means in substantially horizontally spaced relation along the length of the vessel means and acting to provide a plurality of substantially parallel paths for material flow;
(d) A plurality of agitation means located in the spaces before and after each of the parallel plate assembly means along the length of the vessel means and acting to facilitate contact between the materials present in each of these spaces;
(e) A parallel plate separation means located in the vessel means downstream from the parallel plate assembly means to separate a relatively heavy material and a relatively light materail;
(f) First outlet means for removing the relatively light material from the vessel means; and
(g) Second outlet means for removing the relatively heavy material from the vessel means.
The present apparatus preferably further comprises substantially stationary base means acting to substantially eliminate material flow beneath and around the parallel plate assembly means.
The present apparatus offers many advantages. Firstly, the ease of fabrication. The vessel means is trough-like and easily fabricated from plates of metal, thermoplastic, concrete, fiberglass composite, or other materials commonly used to fabricate vessels. There are few openings below liquid level of fabricate, leak, or require service. Also, there are a minimum of moving parts because no pumping is required between agitated spaces (stages) (this is very important when handling abrasive solids) and the drive or drives preferably used to power the agitation means are accessible high and dry above liquid level with no liquid-tight shaft-seals required as there are with side-entry agitators on many extraction column designs. Agitation can easily be varied from space to space (stage to stage) to meet process requirements, and the extraction unit can be built with as many spaces (stages) as needed without height restrictions as it is substantially horizontal and easily supported on the ground.
Secondly, the operation of the unit is simple and flexible enough to meet varied process requirements. The extractor can easily be adapted to be either co or counter current, and will process either light or heavy solids phase dispersed in the liquid phase or be used for liquid/liquid extraction. Residence time of materials can be altered from space to space (stage to stage) to meet process requirements by, for example:
(1) Varying the horizontal distance between parallel plate assembly means to vary the agitated space between the assemblies;
(2) Adding to or subtracting grom the area of a flow path of the parallel plate assembly means accessible to material flow (e.g., use a flow blocker means as described herein).
The smaller this accessible area, the more material is randomly denied access to the next space (stage), thereby raising the concentration of that material in a given agitated volume, e.g., upstream from the flow blocker means;
(3) Varying the angle formed by a line connecting the tips of the plates in a given parallel plate assembly means and vertical to provide more of less (as desired) horizontal area of open flow passages between the plates available for descending material to enter and travel the flow passages to the next agitated space (stage) and/or
(4) Entry baffles means to control the turbulence of the material entering one or more of the parallel paths of a given parallel plate assembly means. Although there are many combinations possible, in general many large entry baffles make very still areas so that very fine and slow settling materials will get the time free from agitator turbulence to descend into the flow paths between the parallel plates. No entry baffles or a few small entry baffles would suffice for heavy hard-to-suspend particles by blocking just enough turbulence to allow them to quickly fall into the flow channels.
The use of parallel flow channels between substantially horizontally spaced agitated spaces (stages) eliminates the need to separate and collect material for transfer to the next stage as is often done (see U.S. 4,268,484 and U.S. 4,292,277 and U.S.S.R. Patent Document 891,109), so that the materials continue to be in intimate contact even while transferring from stage to stage, offering better contact efficiency. In other words, the present agitation means and parallel plate assembly means act together so that the first and second materials continue to be in intimate contact even while transferring from space to space. Also, the sloped flow paths of the present extractor allows operation with dense solid phase while designs relying on overflow weirs to control flow between stages are thus limited to liquids-only operation.